They should not freeze your bank account in an IVA --- this has probably been done in error as it is common in bankruptcy and many bank staff (surprisingly) do not seem to know the difference ! Some banks will close the account, if they are a creditor and a couple will do so regardless (notably HSBC and First Direct).
Who are you banking with and are they a creditor ?
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk